The invention refers to a method for conveying plastic granulates.
German Offenlegungsschrift 2,742,297 discloses a drying container into which granulates to be dried are fed. Dried air is also fed to the drying container, which is passed through the granulates in a counterflow for drying the granulates. The moisture carried with the exhaust air from the drying container is removed from the exhaust air outside the drying container. A portion of the dried air to be fed to the drying container is utilized for conveying the dried granulates discharged from the drying container to a place of subsequent processing, e.g. a feeder for a barrel extruder.
This type of conveying the dried granulates has disadvantages in a number of aspects. Firstly, a portion of the dried air is continuously withdrawn from the otherwise closed loop of the stream of air, comprising the drying container and a device for removing moisture from the air. Therefore, a corresponding replacement portion of fresh air has to be introduced into said loop which results in additional load for the moisture adsorbing material within the exhaust air drying device. Secondly, the throughput of air through said closed loop has to be greater than necessary for drying the granulates within the drying container. This means a higher conveying demand for the blower included in said loop. This leads to a bulky overall apparatus and to waste of energy.
The company Laboratorie-Teknik, Frederikssund, Denmark distributes a drying container for drying granulates by dried air with a designation MDD 120. This device allows conveying dried plastic granulates from the drying container to a subsequent processing machine by a portion of the dried air which is continuously withdrawn form the closed loop of air and re-fed to said loop after conveying of the dried granulates has been effected. This device needs a blower for a greater air throughput than necessary for drying the granulates within the drying container.
German Patent Specification 2,354,745 discloses a method for drying plastic granulates. The drying process of the granulates is interrupted for regenerating the moisture adsorption material contained within a device for removing moisture from the exhaust air of the drying container. The time period for regenerating the adsorption material lasts usually for a approximately a quarter of an hour. For carrying out this method a reversible blower and a number of flap valves are necessary for alternatingly drying the plastic granulates and regenerating the adsorption material.
The "Maschinenmarkt" dated Nov. 1, 1975, published by Vogel, Wurzburg, West-Germany discloses a so-called Hot Air Dryer, through which hot air is passed in counterflow through plastic granulates sinking through the dryer. The granulates are heated and dried by the hot air. A blower is provided for drawing in air from the atmosphere or exhaust air from said dryer which is heated by heating means to the desired temperature before being fed into the dryer.